Problems passing system properties and parameters when running Java class via Gradle

Question

I am trying to run a command-line Java app via Gradle as part of a quick integration test. I am porting my build scripts from Maven, where this was easily done via exec-maven-plugin. My two big requirements are:

Being able to pass system properties to the executable Java code
Being able to pass command-line args to the executable Java code

Please note that I am not trying to read these properties in the build script, I'm trying to read them in the Java program that the script builds and executes.

I have found two other SO posts that address Java program execution via Gradle: one with an answer that advocates using apply plugin: "application" in the build file and gradle run at the command line, and another with answers advocating that approach as well as using task execute(type:JavaExec) in the build file and gradle execute at the command line. I have tried both approaches and have not succeeded.

I have two problems:

(1) I cannot get the Java executable to read the system properties

Whether I do this:

build.gradle:

apply plugin: 'application'
mainClassName = "com.mycompany.MyMain"

Command line:

gradle run -Dmyproperty=myvalue

Or this:

build.gradle:

task execute (type:JavaExec) {
    main = "com.mycompany.MyMain"
    classpath = sourceSets.main.runtimeClasspath 
}

Command line:

gradle execute -Dmyproperty=myvalue

In either case, myproperty does not make it through. The code that begins running from MyMain.main (...) reads the myproperty system property as null/missing.

(2) I cannot pass command line arguments

This is probably related to the first problem. In exec-maven-plugin, for example, command line args were themselves passed in via a system property. Is that the case with Gradle, or is there another way to pass command line arguments?

How do I get these variables through? Also, is it better to use apply plugin: 'application' or task execute (type:JavaExec)?

systemProperties = System.properties as Map – J. P Jul 12 '21 at 15:49 — J. P, Jul 12 '21 at 15:49

score 143 · Accepted Answer · edited Sep 28 '17 at 19:24

143

Figured it out. The main issue is that when Gradle forks a new Java process, it does not automatically pass the environment variable values along to the new environment. One has to explicitly pass these variables via the systemProperties property of the task or plugin.

The other issue was understanding how to pass command-line args; these are via the args property on the task or plugin. As with the Maven exec-maven-plugin, they should be passed in on the command line via yet another system property, as a space-delimited list that then needs to be split() before setting args, which accepts List objects. I've named the property exec.args, which is the old Maven name.

It seems both the javaExec and application plugin approach are valid. One might favor the application plugin approach if one wants to use some of its other features (automatically putting together a distribution, etc.)

Here are the solutions:

JavaExec Approach

Command Line:

gradle execute -Dmyvariable=myvalue -Dexec.args="arg1 arg2 arg3"

build.gradle:

task execute (type:JavaExec) {

    main = "com.myCompany.MyMain"
    classpath = sourceSets.main.runtimeClasspath 

    /* Can pass all the properties: */
    systemProperties System.getProperties()

    /* Or just each by name: */
    systemProperty "myvariable", System.getProperty("myvariable")

    /* Need to split the space-delimited value in the exec.args */
    args System.getProperty("exec.args", "").split()    
}

Application Plugin Approach

Command Line:

gradle run -Dmyvariable=myvalue -Dexec.args="arg1 arg2 arg3"

build.gradle:

apply plugin: 'application'
mainClassName = "com.mycompany.MyMain"
run {    
    /* Can pass all the properties: */
    systemProperties System.getProperties()

    /* Or just each by name: */
    systemProperty "myvariable", System.getProperty("myvariable")

    /* Need to split the space-delimited value in the exec.args */
    args System.getProperty("exec.args", "").split()    
}

edited Sep 28 '17 at 19:24

akoprowski

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answered May 15 '14 at 22:23

sparc_spread

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3

I think that should be System.getProperties() (capital S). – orlanthi Aug 12 '14 at 04:49
1

If you are using gradle 2.xx, you can also use the following: - `systemProperty "myvariable", "${myvariable}"` – eadjei Aug 20 '14 at 18:43
1

Thank you! I put was trying to run Cucumber tests and wanted to pass environment variables to the JVM. I just put "systemProperties System.getProperties()" in test { } instead of in run { } – Svante Sep 22 '14 at 12:15
Will this come in startup ? i actually need like -Dmyvariable=myvaribale1 – smilyface Jul 02 '15 at 06:20
2

Please note that default split doesn't allow arguments with spaces, e.g. `-Dexec.args="--greeting 'hello there'"` – won't work, need to set another delimiter. – Ivan Balashov Sep 05 '15 at 14:05
2

I am still looking for a more direct method. These methods seem to want to edit/massage the current properties and pass them along. Command line and Java properties for running an application or service are akin to "Context" or "Configuration" setting. It would be better to have a plug-in that does things like "run parameters" as a side-by-side profiles or something. I wouldn't like to try debugging the different options for running a significant program like an Eclipse or Netbeans this way . . . (_I accept that this may be just me of course_) – will Dec 08 '16 at 04:44
2

Note that the line `args System.getProperty("exec.args").split()` seems to throw a `NullPointerException` if no arguments have been provided (e.g. just type `gradle run`). – gbmhunter Jan 29 '17 at 10:29
Passing all properties is not a good idea. For me some stuff did not work anymore inthe application related to locating resources – mhstnsc Mar 20 '17 at 07:35
4

Use: args System.getProperty("exec.args", "").split() to avoid null pointer exception if no args are supplied. For example, even 'gradle tasks' will throw an exception with the suggested build.gradle – Mike Hanafey Jun 11 '17 at 16:34
2

I spent like one day trying to figure out why my gradle code was not working, thank you so much. – SoManyGoblins Dec 13 '18 at 14:46
Glad to help :-) – sparc_spread Dec 13 '18 at 15:48
Wonderfully detailed answer. But the real question seems to be What's the interface between *gradle* and *Spring's java test* environment? To properly alter the configuration of the java test environment there needs to be a structured and well-defined interface between them. Arthur – Arthur Feb 21 '23 at 21:07

score 12 · Answer 2 · answered Mar 30 '16 at 22:56

For those who might not want to pollute your application's system properties by passing unrelated Gradle props, I recommend namespacing your arguments.

tasks.withType(JavaExec) {
    System.properties.each { k,v->
        if (k.startsWith("prefix.")) {
            systemProperty k - "prefix.", v
        }
    }
}

java ... -Dprefix.my.prop=true will pass my.prop

Stan Towianski · Answer 3 · 2018-03-03T02:49:22.577

I'm new to gradle so I needed this and what is working for me with gradle 4.6 seems a little easier for the command line. Instead of parsing 1 arg string you can pass an array of args, and I found a way to pass in all property with one line as well. Combined below:

apply plugin: 'java'
apply plugin: 'org.springframework.boot'    <- for my project

task runApp(type: JavaExec) {
  classpath = sourceSets.main.runtimeClasspath

  main = 'testit.TomcatApp'

  // arguments to pass to the application
  //  args 'myarg1 -rest'    <- came in as 1 string

  args = ["--myarg1 with spaces even", "--myarg2"]

  // and to pass in all -D system property args:
  systemProperties = System.properties
}

gradle run -Dwhatever=xxx -Dmyarg2=hey

// Java reading them:
public static void main(String[] args) {
    for ( int i = 0; i < args.length; i++ )
        {
        logger.info( "** args [" + i + "] =" + args[i] + "=" );
        }
    logger.info( "** -Dwhatever =" + System.getProperty("whatever") + "=" );
    logger.info( "** -Dmyarg2 =" + System.getProperty("myarg2") + "=" );

[main] INFO testit.TomcatApp - ** args [0] =--myarg1 with spaces even=
[main] INFO testit.TomcatApp - ** args [1] =--myarg2=
[main] INFO testit.TomcatApp - ** -Dwhatever =xxx=
[main] INFO testit.TomcatApp - ** -Dmyarg2 =hey=

WesternGun · Answer 4 · 2019-03-04T16:36:36.373

Maybe I am late for the party, but has anyone tried with "set the prop before executing gradle"? I have tested and this works too, apparently.

myVar=myVal gradle test

For example, you can set the active profile like:

SPRING_PROFILES_ACTIVE=dev  gradle test

These also work, apparently:(tested)

set myVar=myVal && gradle test      # for windows
export myVar=myVal && gradle test   # for linux and mac

Be wary that myVar cannot be period-separated; or else only the part before the first period will be taken as key.

Problems passing system properties and parameters when running Java class via Gradle

4 Answers4

JavaExec Approach

Application Plugin Approach

Linked

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